FIELD OF THE INVENTION
The present invention relates in general to an improved metallic material which exhibits high corrosion resistance and, in particular, to a method of and an apparatus of manufacturing such a metallic material which are effective to improve corrosion resistance of magnetic materials and to improve reliability of structural materials, as well as use of such a metallic material.
Examples of conventional processes of forming a thin metallic film include plating (electrolytic plating) which utilizes electric field effect or chemical reaction in a solution, an evaporation process in which a film is formed under a vacuum by heating a metal serving as an evaporation source, and sputtering in which a film is formed from a metallic target by means of bombardment by gaseous particles. However, the electrolytic plating process which employs a solution suffers from technical disadvantages in that impurity ions in the aqueous solution enter the formed film and in that the formed film is physically unstable. The evaporation process is disadvantageous, because it is difficult to form a high purity metallic film due to entering of impurity gas molecules during evaporation. The ion beam deposition process (IBD process) is free from any of the above-mentioned problems, and thus allows the formation of a uniform thin film which contains less impurities.
The floating zone melting process is known as a process for improving the purity of metal.
The IBD process is disclosed in, for example, JP-A-60-231924 and JP-A-61-87871. The former patent discloses a magnetic iron film forming method in which iron having a purity of 99.9% is evaporated as an evaporation source, and at the same time ionized together with nitrogen gas and oxygen gas, and iron ions are irradiated onto a substrate to form a magnetic iron film. The latter patent proposes a method of depositing an organic metal or an alloy of organic metals on the surface of a substrate by irradiating an organic metal compound or a metal evaporation compound with an electron beam or an ion beam.
The ion source device employed in, for example, an ion beam apparatus of processing a method surface, an ion implanting apparatus used in manufacturing semiconductor devices, an ion beam deposition apparatus or an accelerator is constructed such that a substance containing the same elements as desired metal ions is placed in a crucible provided with a heater, and a metal evaporation containing a desired metal ion is generated by heating the crucible. The generated metal evaporation is sent to a discharge chamber to generate a discharge plasma containing metal ions, like the Freeman type ion source. It is described in FIG. 6.25 on page 203 of "Electron/Ion Beam Handbook (No. 2)" edited by the 132nd Committee of Japan Society for the Promotion of Science and published by Nikkan Kogyo Shinbunsha in 1986.
However, in IBD, the process of generating a metal ion beam to form a thin film has not yet been developed. Generation of a thin film of pure metal in the IBD process requires selection of a suitable metal compound used to generate metal ion and the provision of a plasma chamber having a configuration suited to extract the metal ion and to forward it to a substrate.
In addition, the film forming conditions must be set in order to form a film which is sufficiently corrosion-resistant to allow the film to be put into practical use.
Studies have been made about an increase in the corrosion-resistance of a thick metal film, e.g., a thick iron film, formed by the floating zone melting process by increasing the purity of iron. However, an increase in the corrosion-resistance of a thin film, such as a magnetic head film, has not been researched yet. Thus, the method of forming a corrosion-resistant thin metallic film has not been proposed yet, and it is thus difficult to form a corrosion-resistant thin metallic film which is the fundamental structural element of a magnetic film.
Furthermore, in conventional technology, a crucible which is highly heat-resistant and chemically stable at high temperatures is required in order to stably generate desired metal ions over a long time, and the temperature of the crucible must be controlled with a high degree of accuracy in order to maintain the pressure of the metal steam at a fixed value. Consequently, the ion source device has a complicated structure, making reduction in the size thereof difficult. It is also difficult to form a highly corrosion-resistant film.